The present invention relates to ether modified polyester resins and to substrates such as electrical conductors coated therewith. More particularly, the present invention relates to polyetheresters prepared from a dicarboxylic acid, an aliphatic diol, an aliphatic polyhydric alcohol having at least three hydroxyl groups, and an aromatic bis(ether dianhydride).
Polyester resins are well known, for example, as described in U.S. Pat. No. 2,936,296, which patent is incorporated by reference into the present disclosure. Briefly, the polyester resins described therein are the reaction product of (1) a lower dialkyl ester of a member selected from the group consisting of a terephthalic acid and isophthalic acid, and mixtures thereof, (2) ethylene glycol and (3 ) saturated aliphatic polyhydric alcohol having at least three hydroxyl groups. Such polyesters were found to be especially useful as insulation for electrical conductors, particularly as insulation for magnet wires used in electrical apparatus.
Holub et al., U.S. Pat. No. 3,288,759, teaches that polyester resins of the type described in U.S. Pat. No. 2,936,296 can be cured more quickly and at a lower temperature by employing a catalyst system comprising a certain class of tertiary amines and an organic polyanhydride. Holub et al. discloses a variety of dianhydrides which can be used, including aromatic bis(ether anhydrides). However, it is clear from the specification, especially column 6, lines 13-14, that the polyanhydride is employed as a crosslinking agent and is not part of the polyester backbone.
U.S. Pat. No. 3,763,109 to Witsiepe discloses thermoplastic copolyesters which combine rapid hardening rates with superior low and high temperature properties and resistance to solvents and heat aging. Such thermoplastic copolyesters consist essentially of a multiplicity of recurring intralinear long chain and short chain ester units connected head to tail through ester linkages, said long chain ester units being represented by the formula ##STR1## and said short chain ester units being represented by the formula ##STR2## wherein G is a divalent radical remaining after removal of terminal hydroxyl groups from poly(alkylene oxide)glycols having a carbon to oxygen ratio of about 2.0-4.3 and a molecular weight above about 400; R is a divalent radical remaining after removal of carboxyl groups from a dicarboxylic acid having a molecular weight less than about 300; and D is a divalent radical remaining after removal of hydroxyl groups from a low molecular weight diol having a molecular weight less than about 250; with the proviso that the short chain ester units constitute about 66-95% by weight of the copolyester, at least about 70% of the R groups must be 1,4-phenylene radicals, at least about 70% of the D groups must be 1,4-butylene radicals, and the sum of the percentages of the R groups which are not 1,4-phenylene radicals and of the D groups which are not 1,4-butylene radicals cannot exceed about 30%. Witsiepe, however, does not disclose or suggest the presence of aromatic moieties within the ether segment of the polymer backbone.
Boldebuck et al., U.S. Pat. No. 4,074,006, provides a curable resinous coating composition which includes a polyester resin, a relatively small amount of a titanium-containing curing agent, and, optionally, up to about 1 part by weight per 100 parts by weight of resin of a surfactant such as a nonionic alkylarylpolyester alcohol which can be prepared, for example, by reacting octylphenol or nonylphenol with ethylene oxide. Such alkylarylpolyether moiety, however, is not a part of the polyester resin backbone.
Avery et al., U.S. Pat. No. 4,212,791, teaches that compositions comprising poly(alkylene terephthalate), an inert particulate nucleating agent, an oligomeric polyester as crystalization promoter, and a segmented polyester-polyether elastomer, exhibit unique crystalization enhancement. The polyester-polyether elastomers are derived from one or more dicarboxylic acids, one or more long chain glycols, and one or more short chain glycols. The long chain glycols are generally poly(alkylene ether)glycols such as poly(ethylene ether)glycol, poly(propylene ether)glycol, and poly(tetramethylene ether)glycol.
Lee et al., U.S. Pat. No. 4,354,965, assigned to the same assignee as the present invention, discloses polyetheramideimide resins prepared by condensing (A) a combination of anhydrides comprising (i) from 1 to 99 parts by weight of a dianhydride of the formula ##STR3## and (ii) from 99 to 1 part by weight of a tribasic acid anhydride, and (B) 0.99 to 1.01 moles per mole of anhydride of a difunctional organic nitrogen compound.
None of the foregoing references, however, disclose or suggest the use of aromatic bis(ether anhydride) to improve the high temperature properties of polyester resins.